1. Field of the Invention
This invention relates to a plasma display panel, and more particularly to a method and apparatus for driving a plasma display panel that is adaptive for improving a sustain driving margin.
2. Description of the Related Art
Generally, a plasma display panel (PDP) is a display device utilizing a visible light emitted from a phosphorus material when a vacuum ultraviolet ray generated by a gas discharge excites the phosphorus material. The PDP has an advantage in that it has a thinner thickness and a lighter weight in comparison to the existent cathode ray tube (CRT) and is capable of realizing a high resolution and a large-scale screen. The PDP consists of a plurality of discharge cells arranged in a matrix type, each of which makes one picture element or pixel of the screen.
FIG. 1 is a perspective view showing a discharge cell structure of a conventional three-electrode, AC surface-discharge PDP.
Referring to FIG. 1, a discharge cell of the conventional three-electrode, AC surface-discharge PDP includes a first electrode 12Y and a second electrode 12Z provided on an upper substrate 10, and an address electrode 20X provided on a lower substrate 18.
On the upper substrate 10 provided with the first electrode 12Y and the second electrode 12Z in parallel, an upper dielectric layer 14 and a protective film 16 are disposed. Wall charges generated upon plasma discharge are accumulated into the upper dielectric layer 14. The protective film 16 prevents a damage of the upper dielectric layer 14 caused by a sputtering during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film 16 is usually made from magnesium oxide (MgO).
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 provided with the address electrode 20X. The surfaces of the lower dielectric layer 22 and the barrier ribs 24 are coated with a phosphorous material layer 26. The address electrode 20X is formed in a direction crossing the first electrode 12Y and the second electrode 12Z.
The barrier rib 24 is formed in parallel to the address electrode 20X to prevent an ultraviolet ray and a visible light generated by a discharge from being leaked to the adjacent discharge cells. The phosphorous material layer 26 is excited by an ultraviolet ray generated during the plasma discharge to generate any one of red, green and blue visible light rays. An inactive gas for a gas discharge is injected into a discharge space defined between the upper and lower substrate 10 and 18 and the barrier rib 24.
Such a PDP drives one frame, which is divided into various sub-fields having a different discharge frequency, so as to express gray levels of a picture. Each sub-field is again divided into a reset period for uniformly causing a discharge, an address period for selecting the discharge cell and a sustain period for realizing the gray levels depending on the discharge frequency. For instance, when it is intended to display a picture of 256 gray levels, a frame interval equal to 1/60 second (i.e. 16.67 msec) is divided into 8 sub-fields SF1 to SF8 as shown in FIG. 2. Each of the 8 sub-fields SF1 to SF8 is divided into an address period and a sustain period. Herein, the reset period and the address period of each sub-field are equal every sub-field, whereas the sustain period are increased at a ratio of 2n (wherein n=0, 1, 2, 3, 4, 5, 6 and 7) at each sub-field, to thereby display a picture according to the gray levels.
Referring to FIG. 3, a conventional driving apparatus for the PDP includes a first inverse gamma corrector 32A, a gain controller 34, an error diffuser 36, a sub-field mapping unit 38 and a data aligner 40 that are connected between an input line 1 and a panel 46, and a frame memory 30, a second inverse gamma corrector 32B, an average picture level (APL) unit 42 and a waveform generator 44 that are connected between the input line 1 and the panel 46.
The first and second inverse gamma adjusters 32A and 32B makes an inverse gamma correction of a gamma-corrected video signal to thereby linearly convert a brightness value according to a gray level value of the video signal. The frame memory 30 stores data R,G and B for one frame and applies the stored data to the second inverse gamma corrector 32B.
The APL unit 42 receives a video data corrected by the second inverse gamma corrector 32B to generate N step signals (wherein N is an integer) for controlling the number of sustaining pulses. The gain controller 34 amplifies a video data corrected by the first inverse gamma corrector 32A by an effective gain.
The error diffuser 36 diffuses an error component of the cell into adjacent cells to make a fine adjustment of a brightness value. The sub-field mapping unit 38 re-assigns the corrected video data from the error diffuser 36 for each sub-field.
The data aligner 40 converts the video data inputted from the sub-field mapping unit 38 in such a manner to be suitable for making a resolution format of the panel 46, and applies it to an address driving integrated circuit (IC) of the panel 46.
The waveform generator 44 generates a timing control signal using the N-step signal inputted from the APL unit 42, and applies the generated timing control signal to the address driving IC, a scan driving IC and a sustain driving IC of the panel 46.
In such a conventional PDP driving apparatus, the APL unit 42 keeps a power consumption of the PDP constantly and emphasizes a relatively bright area when a brightness of the entire image is low. To this end, the APL is set to be in inverse proportion to the number of sustaining pulses as shown in FIG. 4. In other words, a small number of sustaining pulses are applied when the APL is high, whereas a large number of sustaining pulses are applied when the APL is low. If the APL is set to be in inverse proportion to the number of sustaining pulses, then a power consumption of the panel is kept substantially constantly and a relatively bright area is emphasized when a brightness of the entire image is low.
However, when the APL is set to be in inverse proportion to the number of sustaining pulses, a small number of sustaining pulses are applied at a high APL to thereby cause a problem in that a sustain period fails to be sufficiently utilized. In other words, because a sustaining pulse is applied only in a portion of the sustain period at the high APL, a sustain driving margin is deteriorated. Therefore, in the conventional PDP, emission efficiency at the high APL is lowered in comparison to other cases.
More specifically, since a small number of sustaining pulse is applied at a high APL, the sustaining pulse is applied only at a portion of a predetermined sustain period. Thus, a time interval at which any discharge is not generated (hereinafter referred to as “idle interval”), of the sustain period, is widened at the high APL. If an idle interval is widened, that is, if a time supplied with a sustaining pulse between the current sustain period and the next sustain period is set to be long, then a sustain driving margin is deteriorated. For instance, if the idle interval is widened, then electrical charge particles generated by the previous sustain discharge are wasted due to a re-binding thereof, thereby causing an unstable sustain discharge.